_Nitric Acid._--The presence of nitric acid in the air appears to have been first observed by Priestley at the end of the last century, but Liebig, in 1825, showed that it was always to be found after thunder-storms, although he failed to detect it at other times. In 1851 Barral proved that it is invariably present in rain-water, and stated the quantity annually carried down to an acre of land at no less than 41.29 lbs. But at the time his experiments were made, the methods of determining very minute quantities of nitric acid were exceedingly defective, and Way, by the adoption of an improved process, has shown that the quantity is very much smaller than Barral supposed, and really falls short of three pounds. His results for ammonia, as well as nitric acid, are given in the subjoined table. ---------------------+----------------+----------------+-----------------+ | | Nitric Acid in | Ammonia in | Total Nitrogen | | | Grains. | Grains. | in Grains. | | +-------+--------+-------+--------+--------+--------+ | | 1855. | 1856. | 1855. | 1856. | 1855. | 1856. | +--------------------+-------+--------+-------+--------+--------+--------+ |January | 230 | 1564 | 1244 | 5,005 | 1084 | 4,526 | |February | 944 | 544 | 2337 | 4,175 | 2169 | 3,579 | |March | 1102 | 866 | 4513 | 2,108 | 3995 | 1,945 | |April | 325 | 1063 | 1141 | 8,614 | 1024 | 7,369 | |May | 1840 | 3024 | 4206 | 18,313 | 3939 | 15,863 | |June | 3303 | 2046 | 5574 | 4,870 | 5447 | 4,540 | |July | 2680 | 1191 | 9620 | 2,869 | 8615 | 2,670 | |August | 3577 | 2125 | 4769 | 4,214 | 4870 | 4,021 | |September | 732 | 1756 | 3313 | 5,972 | 2917 | 5,373 | |October | 4480 | 2075 | 7592 | 3,921 | 7414 | 3,767 | |November | 1007 | 1371 | 3021 | 2,591 | 2749 | 2,489 | |December | 664 | 2035 | 2438 | 4,070 | 2180 | 3,352 | +--------------------+-------+--------+-------+--------+--------+--------+ |Total in pounds for}| | | | | | | |the whole year }| 2.98 | .280 | 7.11 | 9.53 | 6.63 | 8.31 | +--------------------+-------+--------+----------------+--------+--------+ No attempts have been made to determine the proportion of nitric acid in air, but its quantity is undoubtedly excessively minute, and materially smaller than that of ammonia. At least this conclusion seems to be a fair inference from Way's researches, as well as the recent experiments of Boussingault on the proportion of nitric acid contained in rain, dew, and fog, made in a manner exactly similar to those on the ammonia, already quoted. According to his experiments an imperial gallon contains--